In general, construction equipment is utilized for various uses, such as excavation or transfer of heavy things in a construction field and an industrial field, and is generally divided into wheel construction equipment and caterpillar construction equipment according to a travel scheme.
Here, the construction equipment generally refers to an excavator, a wheel loader, a forklift truck, a back hoe, and the like, and includes an engine, a hydraulic pump generating hydraulic pressure by using power of the engine, a control unit controlling the hydraulic pressure generated by the hydraulic pump by using a hydraulic valve, and an actuator operated by the controlled hydraulic pressure.
Particularly, the construction equipment operates each actuator, for example, the actuator operates a boom, an arm, and a bucket, according to the control of a flow rate and a hydraulic pressure, to perform predetermined work.
Here, as technology for controlling a flow rate and a hydraulic pressure, an open-center flow control system and a load sensing hydraulic system have been known.
The open-center flow control system has a negative flow control scheme, in which a pressure generated at a front end of an orifice is applied to a flow control unit by a flow rate passing through a center bypass and flowing into a tank to control a swash plate angle of a pump, and a positive flow control scheme, in which a pilot pressure of a joystick is selected and applied to a flow control unit to control a swash plate angle of a pump, and the aforementioned two control schemes are configurations in which a discharge flow rate of the pump is divided into a center bypass flow path and an actuator flow path at a part, at which a worker performs a precise operation.
On the other hand, it is known that in the load sensing hydraulic system, an excessive flow rate is not generated, and a flow rate may be distributed regardless of a load of the actuator through a pressure compensator.
The aforementioned technology of controlling a hydraulic pressure and a flow rate is mechanically implemented, so that there is a problem in that a degree of freedom of a control is limited, and it is necessary to always excessively operate the pump and the engine operated in response to an operation of the actuator, so that fuel efficiency is degraded.
In the meantime, the construction equipment is generally used in various work conditions as described above, so that an engine in accordance with a work condition and a means for setting an output of a hydraulic pump need to be included.
That is, pre-stored target revolutions per minute (RPM) of the engine, an RPM of the engine according to an input torque of the hydraulic pump, and an input torque of the hydraulic pump are set according to each work environment.
Accordingly, since an engine throttle lever always maintains a predetermined value regardless of a work speed of a worker or a load degree, fuel is unnecessarily consumed and noise and vibration are generated.
In order to solve the problem, a method of setting a low RPM of an engine in no-load, detecting a load of the engine by a load detecting means, and outputting an RPM of the engine in accordance with the load of the engine has been suggested.
An excavator in the related art uses an open center scheme or a load sensing scheme, and a means for variably controlling an engine and the like, and in this case, in order to automatically control a work apparatus of the excavator, the excavator uses a method of attaching an angle sensor to a connection portion of the work apparatus, and storing information of each angle sensor of a work section, which a worker instructs to store, and reproducing the stored information, or a method of storing a work trace by using a stroke sensor and implementing and correcting the stored work trace.
However, the aforementioned method is influenced by a work environment, such as a characteristic of equipment including each actuator or an angle sensor, a road state, and a load, so that a reproduction property is degraded, and thus an original function is easily lost.